1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to the shape of an island of a resin encapsulated semiconductor device in which a plurality of semiconductor pellets are mounted on one island.
2. Description of the Related Art
An arrangement of a resin encapsulated semiconductor device obtained in accordance with a prior art technique will be described with reference to FIGS. 1 and 2.
FIG. 1 is a plan view of a conventional semiconductor device after wire bonding in which one package has one island and a plurality of pellets are mounted on this island, and FIG. 2 is a sectional view taken along the line II--II of FIG. 1.
Generally, to fabricate a resin encapsulated semiconductor device in which a plurality of pellets are mounted in one package, as shown in FIG. 1, a plurality of pellets 1 are mounted on one island 3. Then, the pellets 1 and inner leads 4 are bonded with each other through bonding wires 2, and one pellet 1 is directly bonded with other pellets 1 through bonding wires 2. Subsequently, the obtained structure is encapsulated with an encapsulating resin, as shown in FIG. 2.
Resin encapsulation will be described with reference to FIG. 2 (a sectional view taken along the line II--II of FIG. 1 which shows the flow of the resin during resin encapsulation).
The encapsulating resin which has gelled upon heating is injected through an encapsulating gate 5, as indicated by arrows of FIG. 2, to start filling.
The encapsulating resin injected from the encapsulating gate 5 flows as indicated by a "resin flow 6" shown in FIG. 2.
The encapsulating resin moves at a predetermined speed until reaching the pellets 1 and the island 3. Then, the flow of the encapsulating resin dividedly fills the portions above and under the island 3. The divided encapsulating resin flows merge after reaching the edge of the island 3 and the flow fills up to the end of the package, thereby completing resin encapsulation.
As a lead frame for mounting a semiconductor chip having a large area on its island, a lead frame having an island divided into a plurality of blocks that are connected with each other through bent portions is proposed (refer to Japanese Patent Application Laid-Open No. 2-207561).
When a semiconductor chip having a large area (size) is to be adhered on the island, since the island is divided into blocks, the stress generated by adhesion and the warp caused by the stress can be decreased.
Other than the above semiconductor devices, another conventional resin encapsulated semiconductor device is proposed, as shown in FIG. 3 (a plan view after wire bonding is completed, which explains another example of the prior art technique). According to this proposal, a plurality of semiconductor chips (pellets 1) are mounted on a plurality of islands 3 corresponding to the pellets 1. The plurality of pellets 1 are not directly bonded with each other, but are wire-bonded with each other through relay inner leads 4a (refer to Japanese Patent Application Laid-Open No. 3-218059).
In the conventional resin encapsulated semiconductor device shown in FIG. 3, the plurality of pellets 1 are not directly bonded with each other, but are wire-boned with each other through the relay inner leads 4a. In this case, a gap corresponding to at least two bonding wires 2 in the longitudinal direction is necessary between the adjacent pellets 1.
Since the number of the relay inner leads 4a is limited due to the limited space, the number of the bonding wires 2 among the pellets 1 is also limited accordingly, which is disadvantageous.
A lead frame for mounting the semiconductor chip, which uses an island divided into a plurality of blocks, aims at decreasing the stress generated upon adhering a semiconductor chip having a large area (size) and the warp caused by the stress, and does not "improve the resin flow during molding", which is the object of the present invention to be described later.
In the conventional resin encapsulated semiconductor device (a resin encapsulated semiconductor device in which a plurality of pellets are mounted on one island) shown in FIGS. 1 and 2, since a portion of the island 3 between the semiconductor chips 1 does not usually have a window, the distance after the resin is divided into portions above and under the island 3 and before merging is long. Thus, the resin filling speeds are different between the portions above and under the island 3. This degrades the filling balance, leading sometimes to floating or sinking of the island.
Also, when the island 3 is particularly thin, the speed of the resin to fill the portion above the island 3 is excessively decreased, so that the resin starts to set during filling. This may cause deformation of the bonding wires.
In addition, when large pellets are to be mounted as the pellets 1, the resin filling balance between the portions above and under the island 3 is not good. Then, floating, sinking, or deformation of the island 3, or deformation of the bonding wires may occur.